Effect of the application of vermicompost and millicompost humic acids about the soybean microbiome under water restriction conditions

Abstract

Humic substances (HSs) are constituent fractions of organic matter and are highly complex and biologically active. These substances include humic acids (HA), fulvic acids (FA), and humin. HS are known to stimulate the root system and plant growth and to mitigate stress damage, including hydric stress. Humic acids have already been reported to increase microbial growth, affecting their beneficial effect on plants. However, there is scarce information on whether HA from vermicompost and millicompost, along with Bradyrhizobium, improves the tolerance of soybean to water restriction. This study aimed to evaluate the responses of soybean plants to the application of vermicompost HA (HA-V) and millicompost (HA-M) along with Bradyrhizobium sp. under water restriction. The experiment was carried out in a greenhouse, and the treatments received Bradyrhizobium sp. inoculation with or without the application of HA from vermicompost and millicompost with or without water restriction. The results showed that HA provided greater soybean growth and nodulation than the control. The application of HA-M stimulated an increase in the richness of bacterial species in roots compared to the other treatments. After the application of water stress, the difference between the treatments disappeared. Microbial taxa were differentially abundant in plants, with the fungal fraction most affected by HA application in stressed roots. HA-V appears to be more prominent in inducing taxa under stress conditions. Although the results showed slight differences between HA from vermicompost and millicompost regarding plant growth, both humic acids promoted an increase in plant development compared to the control.

Co-Inoculation with Bradyrhizobium and Humic Substances Combined with Herbaspirillum seropedicae Promotes Soybean Vegetative Growth and Nodulation

“…Da Silva et al [12] showed that the application of humic acids could help soybean growth through its interference with the endophytic bacteria community, triggering the enrichment of microorganisms with the potential to act both on plant growth and defense against pathogens and abiotic stresses. The modulation of the endophytic and rhizosphere community by humic acids was previously described and can be depicted as a complex process that emerges from different interrelationships between components and functions.…”

“…Earlier reports have also documented a substantial Increase in soybean root dry matter due to HSs, although there was no corresponding increase in the number of nodules [11]. However, more recent studies have shown that soybean plants treated with humic acids can promote plant growth and nodulation compared to control plants by stimulating the abundance of bacterial species in roots [12]. HS' modulation of the rhizosphere community was attributed to the increasing exudation of sugars [13] and other available organic compounds [14].…”

Field Application Study using Vermicompost, Rhizobium and Farm Yard Manure as Soil Supplements to Enhance Growth, Yield and Quality of Glycine max

“…Hungria and Mendes [41] reported that the establishment of soybean in Brazil through the inoculation of Bradyrhizobium strain successfully improved the crop yield and amount of nitrogen fixation. Humic substances from vermicompost have complex and bioactive materials which include humic acids, fulvic acid and humin strongly stimulate the rhizospere and growth of the plant tolerate stress damage including water stress [42]. Humic substances are constituent fractions of organic matter and are highly complex and biologically active.…”